This set includes bacteria diseases

The correct option is Plague, Leprosy, Diphtheria.

To determine why this option is correct, let's analyze the causative agents (pathogens) of the diseases listed in each option to identify which set consists entirely of bacterial diseases:

1. Analyzing the Correct Option:
• Plague: Caused by the bacterium Yersinia pestis.
• Leprosy: Caused by the bacterium Mycobacterium leprae.
• Diphtheria: Caused by the bacterium Corynebacterium diphtheriae.
Since all three diseases in this group are caused by bacteria, this set correctly includes only bacterial diseases.

2. Analyzing the Other Options to See Why They Are Incorrect:
• Malaria, poliomyelitis, mumps: Malaria is caused by protozoan parasites (genus Plasmodium), while poliomyelitis and mumps are viral diseases caused by the Poliovirus and Mumps virus, respectively. None of these are bacterial.
• Mumps, cholera, typhoid: Mumps is a viral disease. While cholera (caused by Vibrio cholerae) and typhoid (caused by Salmonella Typhi) are bacterial, the presence of mumps makes this set incorrect.
• Measles, Tuberculosis, Tetanus: Measles is a viral disease caused by the Measles virus. Even though tuberculosis (caused by Mycobacterium tuberculosis) and tetanus (caused by Clostridium tetani) are bacterial, the presence of measles makes this set incorrect.

Therefore, the only group containing exclusively bacterial diseases is Plague, Leprosy, Diphtheria.